Conventional medical infusion systems utilize a variety of motor technologies for driving the infusion pump such as direct current motors, stepper motors, or solenoid motors. When using such a motor in an infusion pump, safety measures must be designed to protect the user from malfunction of the motor, especially to avoid delivering an excessive amount of a substance or drug, for example insulin, to be infused to the user. This might especially occur in case of a short circuit that bypasses the control system of the motor.
United States Patent Application US 2002/0071225 A1 discloses several solutions for this problem. The first solution is using a motor that needs a multiple of the voltage provided by the battery. In case a short circuit directly connects the motor to the battery, the voltage is not sufficient to drive the motor. A second solution uses a safety circuit that closes the power supply circuit of the pump motor only when a special AC signal is applied to the safety circuit.
The drawback of the first solution is that an expensive and complex DC-DC step-up converter is needed. The drawback of the second solution is that a second dedicated circuit is needed next to control electronics that control the rated supply voltage and therefore the motor in order to regulate the amount of substance or drug to be infused.